The present invention relates generally to DC power supplies, and more particularly to a low-power charge-pumped DC bias supply.
Power supplies are typically designed with their highest operating efficiency at rated load. However, many electronic devices require a low-power bias supply to maintain power to their various electronic circuits when the devices enter either a standby state or a very low-power mode of operation. Consequently, a power supply designed to supply several hundred watts of power when its associated electronic device is in its active state will typically have efficiencies of less than 30% when the electronic device enters a standby state, and efficiencies of less than 10% when the device is in a very low-power mode of operation.
Conventional bias supplies utilize a bridge rectifier coupled to an AC source to supply a full-wave rectified AC voltage waveform to a charge storage capacitor. The voltage waveform is at a relatively high voltage level (1.414xc3x97line voltage), so conventional bias supplies further employ a switch mode bias supply to convert the relatively high voltage to a lower voltage level necessary to power the various electronic circuits which remain active when the associated electronic device is in a reduced power mode of operation. The relatively high voltage level supplied to the bias supply converter increases the cost of the charge storage capacitor as well as the cost of the power converter switch. The relatively high voltages also limit the efficiency of bias supplies to approximately 50% due to voltage and frequency dependant switching losses. Furthermore, current drawn by these bias supplies is rich in harmonics due to the very narrow conduction angle of the diodes and the bridge rectifier.
Many electronic devices, particularly those devices that utilize a very low power mode of operation, would benefit from a low power bias supply that reduces the number of high voltage components required, operates at a high efficiency, is less costly, and reduces generated current harmonics.
The present invention provides a DC power supply. In one embodiment, the DC power supply is a DC bias supply connectable to an AC source. The supply includes first and second input nodes connectable to the AC source. A first capacitor is provided having a first and second terminals. The first terminal of the first capacitor is coupled to the first input node. A pump circuit having first and second output nodes. The pump circuit is coupled between the second terminal of the first capacitor and the second input node. A second capacitor is coupled between the output nodes of the pump circuit. During a first half-cycle of the AC source the pump circuit causes the first capacitor to accumulate a charge and during a second half-cycle of the AC source the pump circuit causes the first capacitor to transfer the accumulated charge to the second capacitor to provide a rectified AC output voltage between the output nodes of the pump circuit.